The present invention relates to a drawing machine for a metal strand, that is a tube or rod. More particularly this invention concerns a device for generally continuously pulling the rod.
In order to reduce the cross-sectional size of a metallic strand, which can be a rod or tube, it is known to engage the strand and pull it continuously, usually through a die. Since the strand normally has a length equal to a multiple of the length of the drawing machine, it must be set up to grip, advance, and release the passing strand in such a manner that it moves continuously.
German 2,852,071 of K. Rehag describes a straight-line pulling system which has two clamps movable along a line on a frame. They work in a hand-to-hand manner so as to continuously advance the strand. Each of the clamps is provided with a two-arm lever which is operated by a respective double cam with both cams on the same actuating shaft.
Another system described in European 0,371,165 of G. Wuller has a rotating drum with arcuate surface ribs that produce the alternate clamp movements.
As a result of the relatively short strokes of the clamps a large portion of each stroke is devoted to getting up to speed and slowing down for reversal. In order to obtain a high average speed, it is therefore necessary to operate at a very high frequency. The mass of the clamps puts however an upper limit on how quickly they can be shuttled back and forth.
It is therefore an object of the present invention to provide an improved drawing machine for a metallic strand.
Another object is the provision of such an improved drawing machine for a metallic strand which overcomes the above-given disadvantages, that is which operates smoothly at a relatively high speed, and that is of simple and reliable construction.
An apparatus for drawing a strand has according to the invention a frame extending in a longitudinal direction, a pair of substantially identical linear motors each having a primary fixed on the frame, and a movable secondary slidable along the respective primary in the direction. The primaries extend parallel to the direction and are transversely spaced on a plane extending in the direction. A strand clamp capable of gripping the strand is fixed between the secondaries. Electricity is supplied to the primaries to longitudinally displace the secondaries and clamp in the frame so that the clamp and any strand held by it are advanced longitudinally through the frame.
Thus a pair of symmetrically arrayed linear motors are used to displace the clamp so that the forces applied to the strand are perfectly balanced to either side and there will be no tipping or canting of the clamps. Another advantage of this is that it is possible to control the speed of the clamp very accurately, moving it downstream at one speed and back upstream at another and very quickly stopping and starting it, something aided by the fat that the linear electric motors are not particularly massive and therefore have little inertia. The secondaries are simple structures, since it is only necessary to generate eddy currents in them as is known for an electric linear motor. The more complex primaries, which typically are formed with coil plates, are fixed. These linear motors are very compact so the overall apparatus can be relatively short.
Normally in accordance with the invention the secondary is about twice as long as the primary. Furthermore the primaries are provided with cooling fins. For servicing the frame has a transversely open longitudinally side. The secondaries can be fixed and the primary movable, but this requires flexible cables and hoses to supply power and coolant to the moving primaries.
In accordance with a particularly effective embodiment of the invention used for hand-to-hand advance of the strand a second pair of substantially identical linear motors longitudinally spaced downstream in the direction from the first-mentioned pair each have a primary fixed on the frame and a movable secondary slidable along the respective primary in the direction. The primaries of the second pair of motors extend parallel to the direction and are transversely spaced along a second plane extending in the direction and crossing the plane of the first motors. A second strand clamp capable of gripping the strand and separate from the first-mentioned clamp is fixed between the secondaries of the second pair of motors. The primaries of the second pair of motors also are connected to the electricity supply. Of course three or more clamps with respective motors on respective planes could also be used.
Each primary according to the invention is of U-section, is generally bisected by the respective plane, and is open inward. Furthermore, U-shaped upstream and downstream mounting plates respectively connect the first and second pairs of drive motors to the first and second clamps. The plates are open toward each other and interfit in a downstream end position of the first clamp and an upstream end position of the second clamp. In this arrangement in accordance with the invention each clamp is flanked by two of the U-shaped mounting plates open away from each other. Thus the two clamps can be brought almost into longitudinal engagement with each other since their linear-motor secondaries are transversely offset and their mounting plates interengage.
According to another feature of the invention the frame comprises a one-piece rail having a pair of downwardly projecting upper ribs provided with the upper primaries and a pair of upwardly projecting lower ribs provided with the lower primaries. The clamps are slidable along the ribs. Such a structure is extremely rigid. In it each clamp has a lower part extending transversely between and bridging the lower ribs and an upper part extending transversely between and bridging the upper ribs. The ribs are angled and extend symmetrically to a vertical center plane.